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Old 04-20-2017, 10:36 AM   #1
67farmtruck
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Ballast Resistor vs. Resistor Wire - 67 250

What is the difference between a ballast resistor (ceramic block with two posts) and a resistor wire, and how do I know which I need? I read a bunch of threads and couldn't figure it out.

I do not see a ballast resistor on my firewall but I do have a cluster of wires emerging from a square black box right next to the choke cable.

I changed out the points, condensor, cap, rotor, and plugs, but no spark. Auto parts guy suggested replacing the resistor first and then the coil, but I don't seem to have a resistor. Could the resistor wire be bad, if in fact that's what I have?

Any advice appreciated!
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Old 04-20-2017, 10:53 AM   #2
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Re: Ballast Resistor vs. Resistor Wire - 67 250

You have a resistor wire. Check it with a voltmeter and see if it's still supplying voltage to your coil. The coil gets voltage through two sources. While the engine is cranking, coil voltage comes from the starter solenoid. When you let the key back to run, it comes through the resistance wire.
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Old 04-20-2017, 10:58 AM   #3
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Re: Ballast Resistor vs. Resistor Wire - 67 250

What exactly is the voltage check and what range of values would indicate a functioning vs. a faulty resistor wire?

With the key in run position, what 2 points do I check voltage across?

So if the coil gets voltage from the starter solenoid with the key in "start", and I'm not getting spark with the key in "start", then the resistor wire could not be the problem....?
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Old 04-20-2017, 11:07 AM   #4
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Re: Ballast Resistor vs. Resistor Wire - 67 250

Key on run, red lead of volt meter to the + terminal on the coil, black lead of voltmeter to a ground. You should see somewhere above 6 volts or so.
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Old 04-20-2017, 11:23 AM   #5
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Re: Ballast Resistor vs. Resistor Wire - 67 250

Much appreciated - I will check that at lunchtime!
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Old 04-20-2017, 11:25 AM   #6
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Re: Ballast Resistor vs. Resistor Wire - 67 250

You bet.

If you do have power to the coil, take a test light and hook it to ground and then put the point on the negative terminal of the coil. Now crank the engine and see if the light flashes.
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Old 04-20-2017, 12:15 PM   #7
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Re: Ballast Resistor vs. Resistor Wire - 67 250

>>Key on run, red lead of volt meter to the + terminal on the coil, black lead of voltmeter to a ground. You should see somewhere above 6 volts or so<<

That would only be true if the engine stopped at a point when the distributor points happened to be closed.
Not much of a test. The test light will give better info, but what are you actually testing for?

Is this a NO START problem? What is the problem that you are trying to diagnose?

There is no electrical difference between a " (ceramic block with two posts) and a resistor wire". Both should have a resistance of 1.8 Ohms for a six cyl chevy distributor.
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Old 04-20-2017, 12:34 PM   #8
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Re: Ballast Resistor vs. Resistor Wire - 67 250

Yes, this is a no start (no spark) problem.

I had it running one day and the next day, no start and no spark.

Points, condensor, cap, rotor, wires, and plugs are all new. Coil is old and I was going to throw in a new one but the auto parts guy suggested checking the resistor first.
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Old 04-20-2017, 01:36 PM   #9
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Re: Ballast Resistor vs. Resistor Wire - 67 250

Put an hei in it and eliminate the resistor wire and the jumper from the starter.
Plus a hotter spark, better idle etc etc..
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Old 04-20-2017, 02:24 PM   #10
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Re: Ballast Resistor vs. Resistor Wire - 67 250

I have 4.8 volts from the coil positive to ground with the key in "run".

The test light flashes from coil negative to ground with the key to "start".

Eventually will put in an HEI but just want it running for a little while first (so my son can drive it to Prom - way better than renting a limo).

Suggested next steps?

Thanks for the input!
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Old 04-20-2017, 02:45 PM   #11
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Re: Ballast Resistor vs. Resistor Wire - 67 250

Have you checked to see if the rotor is turning? (I was unable once to get an engine to start that I had driven the day before and it ended up being a broken timing gear) How did you check for spark? Do the troubleshooting before buying any more parts. (With the quality of the parts today you may be adding a problem) Disconnect the power wire from the coil and measure the voltage to ground. As previously stated you should see 6-8 volts. If not I would check the voltage at the ignition switch. It should be 12 volts. If it is OK then it is probably the firewall connector. If no voltage or less than battery voltage the the switch is suspect number one.
If the voltage at the coil is good then pop the distributor cap and do a careful inspection. The points are just a grounding switch. If your gap is correct then look to see if the ground wire from the breaker plate is intact and securely connected at both ends. Is the wire from the coil good with no cuts or broken spots. If it all looks good disconnect the other wire on the coil and hook a multimeter to it and to ground. Then open and close the points manually. It you don't see a high and low reading on the meter try unhooking the condenser to see if it makes a difference. (You could have a shorted condenser). If the meter never shows conductivity then the points are not closing, the contacts are insulated some way, or maybe there is an open in the wiring. (Could be either the wire to the points or from the breaker plate) If the meter is always showing conductivity then the points are not opening, or the wire to the points is shorted to the case. If so disconnect it from the points and test again. If all this checks out then you may have a bad coil which is easiest to check by swapping a good one in.
I just saw your last post and your volts are pretty low I would concentrate on the power to the coil first. Check the volts at the ignition switch
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Old 04-20-2017, 03:10 PM   #12
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Re: Ballast Resistor vs. Resistor Wire - 67 250

Yes, the rotor turns.

I replaced the other ignition parts recently, although prior to the current problem, so I assumed they didn't suddenly fail.

I'll check the ignition switch voltage. This would be 12V coming out of the switch with the key in "run", right?
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Old 04-20-2017, 08:28 PM   #13
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Re: Ballast Resistor vs. Resistor Wire - 67 250

Yes it should be 12 volts( within a 1/2 volt of whatever the battery voltage is).
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Old 04-20-2017, 08:35 PM   #14
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Re: Ballast Resistor vs. Resistor Wire - 67 250

OK, so now I'm really confused.

I pulled the + wire off the coil - with the switch to "run" I had 12+ volts. So I figured the ignition switch is OK and with the other symptoms, I swapped out the coil.

Now I turn the key and I get I very short burst of power and then nothing. And now the + wire to the coil shows extremely low voltage with the key in "run".

Bad ignition switch after all? Or something else?
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Old 04-20-2017, 09:19 PM   #15
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Re: Ballast Resistor vs. Resistor Wire - 67 250

if your having a hard time diagnosing wiring problem you could try buying one of those ceramic ballast resistors and running a wire from the ign unfused spot on the fuse panel like a hei would put the ballast resistor inline before the coil and try and start it if it starts its in the wiring if not it has to be in the points or condenser . ballast resistor and some wire is fairly inexpensive oh and you will still need to keep the yellow wire from the starter R post so you get 12 volts on start when you switch to hei later down the road you already have the wire in place and eliminate the yellow and ballast
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Old 04-20-2017, 09:34 PM   #16
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Re: Ballast Resistor vs. Resistor Wire - 67 250

from what I understand the resistor either ballast or wire is supposed to give close to 12 volts and as there is a load placed on it , it warms up creating resistance to lower the voltage so the points last longer . the hot spark puts pits in the point contact area and makes for a poor connection in a short time so the need to lower voltage . the 12 volts when it starts coming from the starter R post is only hot while the starter is engaged so it starts in full power for those cold starts . possibly why you get a short burst then it dies out hope this helps
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Old 04-20-2017, 10:01 PM   #17
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Re: Ballast Resistor vs. Resistor Wire - 67 250

=Can't be the points or condensor, can it? I have super low voltage at the + wire to my coil when it's disconnected from the coil. Points and condensor aren't even in that circuit, are they?

Seems like it must be either the ignition wiring or the switch. So I can run a wire from the unfused spot on the panel to the + on the coil with a ceramic ballast inline to bypass my wiring harness?

Appreciate all the insight and knowledge of you all.
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Old 04-20-2017, 10:15 PM   #18
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Re: Ballast Resistor vs. Resistor Wire - 67 250

yes you can and it will tell you if its the wiring or the points or condenser
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Old 04-20-2017, 10:18 PM   #19
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Re: Ballast Resistor vs. Resistor Wire - 67 250

At any moment the points are either open, closed or opening and closing (cranking/running) so you may get different readings.
If I recall, the points closing allows current to flow through the coil primary to ground. Opening collapses the electrical/magnetic field, inducing high voltage on the secondary side, causing spark.

The system was designed for 6V so when 12V came around, points got cooked so they introduced a resistance to limit current. Or so I've read... Note current is limited because on points open, you should read 12V at the coil side of the resistance wire. An open always reads source voltage.

I think I'd pull a plug ground it and check for spark.
You can also jump around the resistor wire w/ a not resistance wire temporarily.
I'd also measure battery voltage across the terminals. A charged battery is 12.6V or more. Load it by say turning on the likes for some seconds first. Less than 12.6V is a battery in need of a charge.
Finally, condensers (capacitors actually) are in there to reduce arcing and wear on the points. A bad condenser can cause weak/no spark because current flow isn't interrupted.
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Old 04-20-2017, 10:23 PM   #20
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Re: Ballast Resistor vs. Resistor Wire - 67 250

Quote:
Originally Posted by 67farmtruck View Post
=Can't be the points or condensor, can it? I have super low voltage at the + wire to my coil when it's disconnected from the coil. Points and condensor aren't even in that circuit, are they?

Seems like it must be either the ignition wiring or the switch. So I can run a wire from the unfused spot on the panel to the + on the coil with a ceramic ballast inline to bypass my wiring harness?

Appreciate all the insight and knowledge of you all.
Yes you can by pass the factory wiring that way. You will need to put a switch in so you can shut the engine off and de-energize the coil when parked. Be sure you tape off or otherwise insulate and secure the factory wire to the coil so it won't short out.
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Old 04-20-2017, 10:27 PM   #21
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Re: Ballast Resistor vs. Resistor Wire - 67 250

Quote:
Originally Posted by HO455 View Post
Yes you can by pass the factory wiring that way. You will need to put a switch in so you can shut the engine off and de-energize the coil when parked. Be sure you tape off or otherwise insulate and secure the factory wire to the coil so it won't short out.
not if you use the ign unfused tap in the fuse box it looses power with key off that's why everyone uses it for hei
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Old 04-21-2017, 12:54 AM   #22
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Re: Ballast Resistor vs. Resistor Wire - 67 250

I had the same symptoms with my 74. I had pertronix and hei in this truck but I like to keep the points in a 6 cyl I found my resistor wire exposed and corroded in a few places. I replaced the resistor wire right from the bulkhead with a 14 or 12 I think and run to a ceramic resistor on the firewall. Also wired to the starter like stock. Definitely starts and idles way better. It was a Chrysler application and I want to say 1.6 or 1.8 ohm. It was 12$ compared to 6-12$ a foot for the resistor wire for 6 or 8 feet.
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Old 04-21-2017, 01:04 AM   #23
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Re: Ballast Resistor vs. Resistor Wire - 67 250

>>I pulled the + wire off the coil - with the switch to "run" I had 12+ volts.<<
As you should. You should get this same voltage with the + wire connected, but only when the points happen to be "OPEN".

Earlier you said, >>I have 4.8 volts from the coil positive to ground with the key in "run".<< Obviously when you read the 4.8V, the points happened to be closed.


>>Now I turn the key and I get I very short burst of power and then nothing.<<

POWER??????

>>I have super low voltage at the + wire to my coil when it's disconnected from the coil.<<

What super low voltage? Earlier you said you had 12+ volts.


>>Can't be the points or condensor, can it? <<

You stand a better chance of having a BAD, NEW Chinese made condenser, than having a GOOD 30 year old condenser.

Did you check the dwell when you installed your new points and then check the timing afterward?
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Old Yesterday, 10:43 PM   #24
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Re: Ballast Resistor vs. Resistor Wire - 67 250

Things keep getting worse.

I thought the resistor wire was the problem so I bypassed it with a wire from the unfused ignition port to the coil +, with an inline ceramic resistor. Now I have only +1.2 volts at my unfused ignition port with the key in "run". Previously I had +12.

Where is the power going? My battery is brand new and reads +12.6. Is my ignition switch bad?
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Old Yesterday, 11:03 PM   #25
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Re: Ballast Resistor vs. Resistor Wire - 67 250

check the red 12 guage wire to the key switch make sure its 12 v that's the input wire to switch then all the rest are out from the switch
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